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Initial conditions in CFX 5.5

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Old   December 18, 2001, 02:22
Default Initial conditions in CFX 5.5
  #1
Astrid
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Hi All,

I would like to study the mixing of a hot and a cold fluid. Initially there are two separate containers, one cold, one hot. At t=0 the get connected. See the figure below.


____ ____
| | | |
| | | |
| |___| |
|hot ___ cold|
| | | |
| | | |
|____| |____|



My question is how to set the intial temperature distribution in CFX 5.5.

Any suggestion? Thanx, Astrid
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Old   December 18, 2001, 14:31
Default Re: Initial conditions in CFX 5.5
  #2
Robin Steed
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Hi Astrid,

A step function will allow you to initialize your fluid temperature with a sharp boundary between hot and cold fluids. The syntax is pretty simple, just make sure the value within the step function is dimensionless. A step function evaluates to zero when the value is negative, one when the value is positive, and 1/2 when the value is zero. Here's an example:

initial_T = 350 [K] - step((x - 2 [m])/1 [m])* 50

This would create a step change from 350 Kelvin down to 300 Kelvin, at x = 2 meters. The divide by 1 [m] makes the term within the step function dimensionless.

Regards, Robin
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Old   December 18, 2001, 16:37
Default Re: Initial conditions in CFX 5.5
  #3
Astrid
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Hi Robin,

This was one of the routes I had in mind.

I am still in a kind of 'CFX4-mind': giving different blocks a different initial temperature. I was trying to define two domains with two different temperatures but had no success. Can you confirm this a route to nowhere?

Thanx, Astrid
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Old   December 18, 2001, 23:24
Default Re: Initial conditions in CFX 5.5
  #4
Robin Steed
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Hi Astrid,

If you only have one subdomain, there is also a function, subdomain, which has a value of 1 in a subdomain and zero elsewhere.

Other than that, CEL will have to do.

Robin
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